At present, there is generally employed the SMPTE-259M standard, i.e., Serial Digital Interface (below, referred to as “SDI”) standard as transmission method of digital video signals in broadcasting stations of all the countries in the world. It is known that the SDI standard is prescribed by the SMPTE (Society of Motion Picture and Television Engineers), and provides that digital data including video data and audio data are converted into serial data to be transmitted.
Referring to FIG. 13, a concrete description will be given to a digital data transmission method under the above-described known SDI standard. It is noted that a description will be given to a transmission method corresponding to television signals of the NTSC system in the following description.
FIG. 13 is an explanatory diagram showing a configuration of one frame in the SDI standard. It is noted that a straight line H of FIG. 13 represents a horizontal pixels of a television signal, and each numeric value on the straight line H represents a pixel number. A straight line V of the same figure represents a vertical line of a television signal, and each numeric value on the straight line V represents a line number.
As shown in FIG. 13, in the SDI standard, one frame period is divided into a horizontal blanking period, and a vertical blanking period, an optional blanking period and an active video period in each field of a first field and a second field constituting the one frame.
The horizontal blanking period is prescribed by the section of horizontal pixels of which the pixel numbers range from 1440 to 1715. The horizontal blanking period is provided with EAV (End of Active Video) and SAV (Start of Active Video) on its top portion and end portion, respectively. In the horizontal blanking period between the EAV and SAV, ancillary data such as audio data and user data can be transmitted.
In the active video period, video data of 1440 pixels are multiplexed on every line to be transmitted as the serial data by a predetermined clock frequency. It is noted that one pixel is comprised of 8 bits or 10 bits of video data.
The optional blanking period is a period which is included in the vertical blanking period. However, the optional blanking period can arrange and transmit video data in the same manner as in the active video period.
The use of the SDI standard enables the transmission of 4:2:2-component television signals of one channel not through analog transmission system, ensuring the prevention of degradation in the signals.
On the other hand, in the case where the video data obtained from digitization of video signals were processed as they were, the video data were increased in amount of data, so that the video data were required very high data rate (transmission rate). Accordingly, when the above-described video data were recorded on a recording medium such as magnetic tape, it was impossible to ensure a sufficient recording time.
In contrast, the handling of the video data by performing compression thereof in such manner that visual image degradation is not recognized by bit rate reduction has been known as effective technique. Concretely, there is a DV format prescribed by the HD digital VCR Committee (High Definition Video Cassette Reorder Committee), and described in “Specifications of Consumer-Use Digital VCRs using 6.3 mm magnetic tape” as the one in which the bit rate reduction of a video signal is applied to a home digital VTR.
In the DV format, data compression is performed in two modes according to television signals by means of bit rate reduction based on DCT (Discrete Cosine Transform). Concretely, in the DV format, a standard television signal is compressed to 25 Mbps data, while a high-definition television signal is compressed to 50 Mbps data. The compressed video data are recorded on the magnetic tape with interleaved audio data, VAUX data which are data ancillary to the video data, AAUX data which are data ancillary to the audio data, and sub-code data and the like. In the case where the data compressed in the 25 Mbps mode are recorded on the magnetic tape, the data for one frame are divided into 10 tracks of the magnetic tape to be recorded. Also, in the case where the data compressed in the 50 Mbps mode are recorded on the magnetic tape, the data for one frame are divided into 20 tracks of the magnetic tape to be recorded. It is noted that, as for the concrete information the above-described VAUX data, AAUX data and sub-code data show, it is described in, for example, the technology of “digital recording and reproducing apparatus” disclosed in Japanese Laid-Open Patent Publication No. 7-226022.
When the video data compressed by the bit rate reduction such as the DV format are transmitted using the above-described SDI standard, in the prior art, the compression of the video data has been required to be once decompressed back into a base band signal. Because in the SDI standard, there is prescribed the transmission method of not the compressed video data but the non-compressed video data which have not been compressed. Further, the SDI standard is intended to transmit the video data of the one channel, and hence it has no provisions for the transmission method for transmitting multi-channel video data. For this reason, for example, transmission of compressed multi-channel video data between recording and reproducing apparatuses by the use of the SDI standard has required that a transmission line was provided for every channel, and further that at least a decoder and an encoder were provided at the transmission line on the transmitting side and the receiving side, respectively.
Examples of a conventional digital data transmission method to overcome the forgoing problems include the technology of “digital data transmission method” disclosed in Japanese Laid-Open Patent Publication No. Hei 9-46705. The object of the conventional digital data transmission method is to transmit multi-channel video signals compressed by, for example, the DV format, utilizing the existing transmission lines comprised of coaxial cables.
Here, a concrete description will be given to a conventional digital data transmission method with reference to FIG. 14.
FIG. 14 is an explanatory diagram showing a method for multiplexing and transmitting digital data of six channels using the SDI standard in a conventional digital data transmission method.
As shown in FIG. 14, in the conventional digital data transmission method, the active video period is divided into units of 240 pixels (words), so that six transmission areas are formed on the SDI standard. Six channels 1, 2, 3, 4, 5, and 6 are assigned to the six transmission areas, respectively. In each of the channels 1 through 6, digital interface data (below, referred to as “DIF data”) for the one frame are arranged. Specifically, the DIF data are comprised of a plurality of a DIF block, and the DIF data are arranged in the transmission area so that three DIF blocks are multiplexed on every line. The DIF data are also comprised of the video data compressed to the 25 Mbps based on the DV format, the interleaved audio data, the VAUX data, the AUUX data and the sub-code data.
With the conventional digital data transmission method, in the case where the data compression is performed in the 25 Mbps mode as shown in the same figure, it is possible to multiplex the DIF data up to a maximum of the six channels of the channels 1 through 6 and transmit them on the SDI standard. Also, in the case where the data compression is performed in the 50 Mbps mode, two transmission areas can be assigned per one channel to multiplex the DIF data and transmit them on the SDI standard.
The DIF data for the one frame are comprised of a plurality of a DIF sequence. The DIF sequence is a transmission unit defined by the DV format. In the case of the 25 Mbps mode, one DIF sequence corresponds to one track on the magnetic tape. Also, in the case of the 50 Mbps mode, the one DIF sequence corresponds to two tracks of the magnetic tape.
A concrete description will be given to the transmission order of the DIF blocks constituting the DIF sequence with reference to FIGS. 15 and 16.
FIG. 15 is an explanatory diagram showing a concrete example of the transmission order of DIF blocks in the case of a 25 Mbps mode. FIG. 16 is an explanatory diagram showing a concrete example of the transmission order of the DIF blocks in the case of a 50 Mbps mode. Each transmission order of the DIF blocks shown in FIGS. 15 and 16 is the same one as that described in the technology of the foregoing Japanese Laid-Open Patent Publication No. Hei 7-26022.
As shown in FIG. 15, in the case of the 25 Mbps mode, the DIF sequence has a header DIF block H0, sub-code DIF blocks SC0 and SC1, VAUX DIF blocks VA0 to VA2, audio DIF blocks A0 to A8, and video DIF blocks V0 to V134. These DIF blocks are, as shown in the same figure, sequentially transmitted in the order of transmission shown by an arrow of the figure. Each the DIF has 80 bytes of data.
Next, in the case of the 50 Mbps mode, processing is performed by using the processing system in the 25 Mbps mode in two-system parallel. That is, data of the odd-numbered tracks of 20 tracks corresponding to data for one frame are processed by the one processing system, while data of the even-numbered tracks are processed by the other processing system. Hereinafter, the data corresponding to the odd-numbered tracks are defined as sub-channel A, while the data corresponding to the even-numbered tracks are defined as sub-channel B.
Specifically, first, in the data processing of the video signals in the 50 Mbps mode, the one frame is divided into two areas. Then, the data of the one area are processed as data of the sub-channel A, while the data of the other area are processed as data of the sub-channel B. Therefore, in the video signals, the bit rate reduction encoding and decoding processing are performed independently in each of the sub-channels A and B. Also, in the audio signals, 1 and 3 channels of four channels are divided into the sub-channel A, while 2 and 4 channels are divided into the sub-channel B, thus performing processing.
Subsequently, in the case of the 50 Mbps mode, after data processing is performed between the sub-channels A and B as described above, as shown in FIG. 16, the respective DIF blocks of the sub-channels A and B are arranged alternately, and thus multiplexed, thereby performing a sequential transmission by the order of transmission shown by an arrow of the figure.
However, in the foregoing conventional digital data transmission method, as shown in FIG. 14, the DIF blocks of each channel are multiplexed and transmitted sequentially three by three within one line. Accordingly, in this conventional digital data transmission method, in the case where data of a plurality of channels are transmitted, each data of a plurality of channels is sent out from the transmitting side to the receiving side of a transmission path with being mutually mixed within one line. Consequently, in the conventional digital data transmission method, data cannot be processed in the order inputted in the receiving side of the transmission path. This requires, for example, that the received data be held until the data for one frame has been input.
Concretely, the case is conceivable where data are transmitted at high speed from a digital data recording and reproducing apparatus as application for transmitting the digital data of a plurality of channels including the video signals subjected to the bit rate reduction through a digital interface. That is, the data is reproduced from the recording medium at high speed such as 4 times normal speed. Then, the data of four channels are multiplexed and transmitted on the transmission path in accordance with the above-described SDI standard and the like. This enables a reduction of time required for data transmission down to ¼. In this case, with the video signals of the same material, data of four chronologically consecutive frames are multiplexed and transmitted in the active video period of the one frame as data of four channels, respectively. However, in the conventional digital data transmission method, the data of the four frames are not arranged in the chronological order on the transmission path. Accordingly, in an apparatus of the receiving side for receiving data transmitted at high speed such as recording and reproducing apparatus, there has arisen a problem that data processing cannot be performed in the order inputted.
Further, in a system for transmitting data of a plurality of different materials simultaneously, the use of conventional digital data transmission method cannot enable the multiplexing and distribution of, for example, a plurality of data reproduced from their respective different recording and reproducing apparatuses on a digital interface. This is because as shown in FIG. 14; in the conventional digital data transmission method, the data of each channel are multiplexed within one line. Further, the data of each channel are arranged over a plurality of lines, and two fields. For this reason, the multiplexing and distribution of a plurality of data cannot be performed on a line-by-line basis, or on a field-by-field basis using the conventional digital data transmission method.
Further, in the conventional digital data transmission method, as shown in FIGS. 15 and 16, the arrangement of data within the channel is changed in accordance with the data rate of the data to be transmitted. For example, in the case of the above-described 50 Mbps, the data are transmitted using the same transmission area as that in the case of two channels in the 25 Mbps mode. However, in the conventional digital data transmission method, the arrangement of data within the transmission area, that is, the method of multiplexing of data has been changed between the case of the 50 Mbps mode and the case of two channels in the 25 Mbps mode. Consequently, in the conventional digital data transmission method, an increase in kind of multiplexing has required an increase in size of a data multiplexing circuits, and switching of control in accordance with the contents of data to be handled. Especially, in the apparatus on the receiving side, it has been very difficult to change data distribution process according to the contents of the received data and the data rate in real time.